1. Field of Invention
The present invention relates to a liquid crystal device and electronic equipment provided with the same and specifically, to an alignment control technology for a fine homeotropic alignment liquid crystal device suitable for being used in a light bulb in a projector, in a display unit of a mobile phone or a PDA, and so on.
2. Description of Related Art
A display of high-contrast and wide angle of visibility is required in the field of liquid crystal devices. A homeotropic alignment mode is presently being studied to realize such a display. A liquid crystal device of a homeotropic alignment type has a structure in which liquid crystal having negative dielectric anisotropy is enclosed between a pair of opposed substrates. One of these substrates is configured, for example, as an array substrate having a plurality of pixel electrodes arranged in a matrix manner and a TFT for switching each pixel electrode individually. A homeotropic alignment film is formed on the substrate surface.
The other substrate opposed thereto is formed on the entire surface of the substrate with a common electrode formed of a transparent conductive film, such as an ITO, and a homeotropic alignment film is formed thereon. In such a liquid crystal device, in order to reduce or prevent malfunction of the TFT due to a light beam from a light source coming from the side of the opposed substrate, or in order to reduce or prevent color blur between the adjacent dots in case of color display, a light shielding film is provided on the side of the opposed substrate. In particular, when using the liquid crystal device as a light bulb for a projector, the light shielding film as such is inevitable. The light shielding film is formed in a lattice-shape corresponding to the non-pixel areas and is disposed between the substrate body and the common electrode.
In such a liquid crystal device of a homeotropic alignment type, liquid crystal molecules are standing substantially perpendicular to the plane of the substrate due to the existence of the homeotropic alignment film in the initial state of alignment (the state of alignment when no voltage is applied), and this state is used as a black display. Therefore, display of higher black levels and higher contrast ratio than those in the TN type will be realized.
However, the liquid crystal device of a homeotropic alignment type is originally weak in alignment restraining force, and hence is liable to exhibit an unstable domain structure because the liquid crystal molecules are brought into various states of alignment when a voltage is applied thereto. Therefore, there is a case where an area in which the liquid crystal molecules are not fell down (disclination) is generated at a boundary between the adjacent domains, and the disclination area becomes unstable due to slight disarrangement of alignment on the substrate or variations in voltage application. Although it is not a serious problem as long as the disclination area is always generated at the same position, a feeling of roughness is generated on image display if the disclination area moves all over the panel.
In order to prevent deterioration of the image quality, for example, in Japanese Unexamined Patent Application Publication No. 6-301036, a structure in which openings are provided on a transparent common electrode at the positions opposing the centers of the pixel electrodes is proposed. In this structure, the liquid crystal molecules positioned in the area of the openings are hardly affected by an electric field generated between the pixel electrodes and the common electrode by application of a voltage. Thus, the liquid crystal molecules in the area of the openings are maintained in the initial state of homeotropic alignment. Therefore, the orientation of alignment of the liquid crystal molecules has a regularity with which they are aligned toward the center of the pixel. Hence unregulated occurrence of disclination is reduced or prevented, whereby clear image display without roughness is achieved.